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Elastic metamaterial has a great potential in controlling low-frequency elastic waves.Negative material parameters are usually related to internal resonance of material,for example,monopole,dipole and quadruple resonances may produce negative effective bulk modulus,mass density and shear modulus.In this talk,we will explain how to realize elastic metamaterials by promoting rotational resonance with chiral microstructure,elastic metamaterials with simultaneous negative effective mass density and bulk modulus can be easily designed.We first study a mass-spring model of a chiral elastic metamaterial that exhibits simultaneously negative mass density and negative Youngs modulus.Then a chiral lattice with coated inclusions are analyzed and designed to have this double negativity,the tuning of the resulting low-frequency bandgaps is discussed by adjusting microstructure parameters of the coated inclusion and lattice geometry.The capability of the proposed metacomposite beam for the low-frequency vibration suppressing is demonstrated.Finally,a novel chiral microstructure design made of single-phased solid material is suggested.The effective elastic properties of the metamaterial are numerically determined and their relations with the translational and rotational resonances are quantitatively analyzed.Transient elastic wave experiment tests in a plate structure are also conducted to successfully demonstrate the negative refraction of the proposed metamaterial at the designed frequency,which are in good agreement with predictions by the numerical simulation.